JP4323324B2 - Large steel for producing injection molds for plastic materials or for manufacturing parts for metalworking - Google Patents

Description

  The invention relates in particular to a steel block that can be used for the production of molds for the injection molding of plastic materials or of metals such as light alloys, or for the production of metal working tools.

  Generally, a plastic material injection mold is manufactured from steel having a hardness of about 300 HB. However, when these molds are used to mold plastics such as industrial plastics or thermosetting plastics, it is preferable to use harder steels that are more resistant to wear. Therefore, 55NCV7 type steel containing about 0.55% carbon, 1.75% nickel, chromium, molybdenum, and vanadium may be used, making it possible to manufacture a mold having a hardness of about 400HB. Become. However, this steel has a number of drawbacks: difficult to machine and difficult to weld. In addition, the steel often has local segregation that constitutes hard spots that are detrimental to polishing or chemical graining. These two drawbacks are particularly undesirable. This is because mold manufacture requires significant machining, and molds are generally repaired by refilling by welding and then polished or granulated. Furthermore, it must be possible to harden these molds without losing hardness, for example by nitriding.

  For even more demanding applications, it is preferred to use steel that is even harder and more resistant to wear, especially if the injection molded plastic contains very hard fibers. Similarly, the increase in injection molding pressure has led to the search for stronger and therefore harder steels. Finally, for certain applications involving light alloy injection molding, or cold or warm processing of metals, the mechanical stress and wear resistance requirements on the tool have a hardness greater than 450 HB. Requires steel. Thus, a steel with a strength of about 450 or just 500 HB, such as the grades of AISI H11 or H13, commonly used for light alloy injection may be required. These steels contain about 0.4% carbon, 5% chromium, l. Contains 25% molybdenum and 0.3 to 1% vanadium. However, this type of steel has a higher degree of the same drawbacks as 55 NCDV7.

  In addition, the increased hardness causes further problems, particularly critically. It is almost inevitably caused by a decrease in toughness, i.e. between the cooling ducts and the surface of the impression of the mold that should be effectively cooled by passing them relatively close to the surface. Risk of tearing.

  The object of the present invention is for molds that are easier to weld, easier to machine, polish and granulate than prior art steels and yet are better heat conductors Or, by proposing steels for the manufacture of parts for metalworking and enabling the production of parts or tools having a hardness of about 450 HB to over 500 HB, even after surface hardening by nitriding, these disadvantages This means that the required properties, in particular the hardness properties, must be compatible with tempering at least at 530 ° C.

The invention therefore relates to a steel block for the production of mold or tool parts having a thickness exceeding 20 mm and can reach 1500 mm, the structure of which is martensite or martensite. Sight-bainite, the hardness of which is between about 430HB and 520HB in all respects, and the chemical composition of the steel is in weight percent,
0.180% ≦ C ≦ 0.400%
Si ≦ 0.8%
Mn ≦ 2.5%
Ni ≦ 3%
Cr ≦ 3.5%
Mo + W / 2 ≦ 2.8%
V + Nb / 2 + Ta / 4 ≦ 0.5%
Al ≦ 0.4%
Ti + Zr / 2 ≦ 0.1%
-Boron with a content between 0.0005% and 0.015%,
One or more elements from among sulfur, selenium, and tellurium optionally contained, the total content of these elements being 0.2% or less,
-One or more elements from lead and bismuth, optionally included, the total content of these elements being 0.2% or less,
-Optionally containing calcium with a content of 0.1% or less,
The balance is a impurities resulting from iron and manufacturing, copper are impurities, the chemical composition, also satisfies the following equation,
3.2 ≦ Tr ≦ 9
85 ≦ Dr ≦ 95
U / Dr ≦ 10.0
Mo * + 3xV * ≧ 0.4%
In the formula, for the content expressed in%,
Tr = 1.8xC + 1.1xMn + 0.7xNi + 0.6xCr + 1.6xMo * + K,
Where K = 0 if the steel does not contain boron, and K = 0.5 if the steel contains boron,
Dr = 54xC ^0.25 + 24.5x (Mo * + 3xV *) ^0.30 + 1.58xMn + 0.74xNi + 1.8xSi + 12.5x (Cr) ^0.20
U = 1600 × C + 100 × (0.25 × Cr + Mo * + 4.5 × V *),
R = 3.8xC + 10xSi + 3.3xMn + 2.4xNi + 1.4x (Cr + Mo *),
Mo * = Mo + W / 2,
V * = V + Nb / 2 + Ta / 4,
The content of boron, aluminum, titanium, zirconium, and nitrogen, expressed as 1/1000 of the weight percent,

上式で、Ｋ１＝Ｍｉｎ（Ｉ＊；Ｊ＊）、
Ｉ＊＝Ｍａｘ（０；Ｉ）、およびＪ＊＝Ｍａｘ（０；Ｊ）、
Ｉ＝Ｍｉｎ（Ｎ；Ｎ−０．２９（Ｔｉ＋Ｚｒ／２−５））、

Where K1 = Min (I *; J *),
I * = Max (0; I) and J * = Max (0; J) ,
I = Min (N; N−0.29 (Ti + Zr / 2−5)),

である。

It is.

  Preferably, the chemical composition is R> 11.

  Preferably, the chemical composition is R ≦ 2.7 × Tr.

The silicon content is preferably precisely less than 0.45% by weight.

  Preferably, the composition is R / (2.7 × Tr) ≦ 0.90, more preferably R / (2.7 × Tr) ≦ 0.80.

  Preferably, the composition is U / Dr ≦ 9.0.

In addition, the chemical composition of steel is
0.230% ≦ C ≦ 0.350%
Si ≦ 0.30%
0.1% ≦ Mn ≦ 1.8%
Ni ≦ 2.5%
0.2% ≦ Cr ≦ 3%
Mo + W / 2 ≦ 2.5%
V + Nb / 2 + Ta / 4 ≦ 0.3%
Mo * + 3xV * ≧ 0.8%
And even more preferably
0.240% ≦ C ≦ 0.320%
Si ≦ 0.15%
0.1% ≦ Mn ≦ 1.6%
Ni ≦ 2%
0.2% ≦ Cr ≦ 2.5%
0.3% ≦ Mo + W / 2 ≦ 2.5%
V + Nb / 2 + Ta / 4 ≦ 0.3%
Mo * + 3xV * ≧ 1.2%
It is.

  Therefore, the composition is preferably Tr> 4.5.

  The invention also relates to a mold part made of steel that has been machined into a block according to the invention, which steel is at least surface hardened by nitriding and its hardness is 430 HB in all respects. It is between 530HB.

  The steel according to the invention has the advantage of being a better thermal conductor than the steel according to the prior art. This better thermal conductivity allows the cooling duct to be further away from the mold surface than when using prior art steel. Thus, the risk of tearing between the duct and the impression of the mold is substantially reduced. Furthermore, due to the better thermal conductivity, the cooling of the mold is performed more uniformly, which improves the quality of the molded part.

  The steel according to the invention is also intended for the production of metalworked parts.

  The present invention will now be described and illustrated in more detail, but is not limited by the examples.

  Mold or metalworking parts are manufactured by machining a solid block of steel that is quenched to obtain a homogeneous martensite-bainite structure and tempered to obtain the desired properties of hardness and ductility. The Therefore, it is necessary to use steel having high temperability and considerable hardenability. However, these hardened steels must have the best machinability possible and the highest thermal conductivity possible. This last property helps to improve the productivity of the molding operation. These various combinations of properties are initially incompatible. In fact, it is known that the harder the steel, the easier it is to machine and the machinability by adding alloying elements such as sulfur, calcium, selenium, tellurium or lead. Is known to improve. However, the addition of these elements must be limited in mold steels. This is because when the surface of the impression of the mold is granulated, it is accepted, but when the surface is polished, these elements are harmful. In any case, the addition of these elements is inappropriate. It is also known that the thermal conductivity and hardenability of steel change in reverse as a function of its composition. Therefore, these requirements are incompatible. However, the inventor has found in a new way that it is possible to find a range of compositions that result in a combination of properties substantially better than those of known steels. The range of these compositions is determined on the one hand by the spread of the respective content of the elements of the composition and on the other hand by the recipe to be followed.

To obtain a combination of these properties, the steel must contain:
-0.18% to 0.4% carbon, the content of which is preferably 0.230% and 0, in order to produce a hardened carbide without excessively impairing the weldability, toughness and machinability. .Between 350%, more preferably between 0.240% and 0.320%;
Less than 0.8% silicon, preferably less than 0.30%, more preferably less than 0.15%. This element, usually used to deoxidize steel during production, adversely affects thermal conductivity.

However, it is always present at least in trace amounts;
-Less than 2.5%, preferably 0.1 to 1.8%, and more to obtain good hardenability without causing excessive segregation which reduces the ability to obtain a good surface condition in the mold Preferably 0.1 to 1.6% manganese. This element is always present in at least a trace amount. Furthermore, the content is preferably higher than 0.1% in order to capture sulfur which is also present in the state of impurities. If sulfur is added to improve machinability, the minimum manganese content should preferably be matched accordingly, at least 5 times the sulfur content, preferably 7 times. There must be;
-Nickel of less than 3%, preferably less than 2.5%, more preferably less than 2%. This element increases the hardenability but is very expensive. May be present in trace amounts. However, in applications that require greater toughness and very uniform hardness, it may be worth reducing the manganese content in preference to nickel at a ratio of 2 parts nickel to 1 part manganese. Replacing part of this manganese with nickel also has the advantage of reducing segregation;
Less than 3.5% chromium, preferably 0.2% to 3%, more preferably 0.2% to 2.5% chromium. This element increases hardenability, but if it is too much, it will thicken the carbides in the chromium and make it more harmful to other more convenient elements such as molybdenum, tungsten, vanadium, niobium, and tantalum. Tend. Chromium may be present in trace amounts;
-Molybdenum and / or tungsten with a content such that the sum Mo * = Mo + W / 2 is less than 2.8%, preferably less than 2.5%; and it exceeds 0.3% Is also preferable. These elements have a significant quenching effect. In addition, these elements substantially reduce intermediate annealing, and this is desirable when subjected to a surface treatment such that the impression of the mold is nitrided at a temperature of at least 500 ° C. However, if the amount is too large, these elements impair the machinability;
From among vanadium, niobium and tantalum, with a content such that the sum V * = V + Nb / 2 + Ta / 4, if any, is less than 0.5%, preferably less than 0.3% At least one element selected. These elements increase resistance to intermediate annealing, especially when tempering is performed at temperatures higher than 550 ° C. These elements also increase the wear resistance of the impression of the mold. However, if the amount is too large, these elements impair machinability and weldability;
-0.0005% to 0.015% boron. This element substantially increases the hardenability without adversely affecting the thermal conductivity. Furthermore, the effect disappears at the high austenitizing temperatures experienced during welding, which is advantageous for the possibility of good repair by welding. In effect, below the 0.0005% limit of detection by analytical means, it has no significant effect. If it exceeds 0.015%, the steel becomes brittle without increasing the hardenability;
-Optionally included, up to 0.4% aluminum and optionally included one of titanium and zirconium, the sum of which Ti + Zr / 2 may reach 0.1% or Multiple elements. These elements are strong deoxidizers. Furthermore, if the steel contains boron, the nitrogen content must be less than 0.0250%, but these elements are generally less than 0.0250% as impurities, but even less Fix the nitrogen still present at the possible content. For boron to be fully effective, the presence of at least one element from aluminum, titanium, and zirconium is desirable.

  In order to allow the aluminum, titanium, and zirconium utilized in these elements alone or in combination of two or three to protect the boron from nitrogen and thus to make the boron fully effective, The content of boron, aluminum, titanium, zirconium and nitrogen expressed in 1/1000 is

上式で、Ｋ１＝Ｍｉｎ（Ｉ＊；Ｊ＊）、
Ｉ＊＝Ｍａｘ（０；Ｉ）およびＪ＊＝Ｍａｘ（０；Ｊ）
Ｉ＝Ｍｉｎ（Ｎ；Ｎ−０．２９（Ｔｉ＋Ｚｒ／２−５））

Where K1 = Min (I *; J *),
I * = Max (0; I) and J * = Max (0; J)
I = Min (N; N−0.29 (Ti + Zr / 2−5))

でなければならない。

Must.

-Copper may be in trace or impurity form, up to a content of about 0.3%;
-In some cases, one or more elements from small amounts of sulfur, selenium and tellurium, the total content of these elements must be less than 0.200%. However, if the steel is intended for the production of molds with polished, chemically grained surfaces, the total content of these elements is less than 0.025%, or preferably less than 0. Must be less than 005%;
-Optionally one or more elements from lead and bismuth, the total content of these elements being less than 0.2%. However, if the steel is intended for the production of molds having a polished and chemically granulated surface, the steel preferably does not contain such elements;
-Calcium with a content of less than 0.100%, optionally included. However, if the steel is intended for the production of a mold having a polished, chemically grained surface, it is preferred that the steel does not contain this element. This is because its clear effect on machinability is achieved with sulfur, which is preferably limited if the steel has to be polished and granulated.

  The balance of the composition consists of iron and impurities from production. For all alloying elements for which no minimum content is imposed, even if these elements are not added, they are still found in the form of at least very low content residues or impurities Note that there is a possibility.

Finally, within the limits that have just been clarified, the steel composition must be selected in order to obtain the desired properties for use. For this purpose, its composition must be as follows:
-Tr = l. The value of 8xC + 1.1xMn + 0.7xNi + 0.6xCr + 1.6xMo * + K in the formula is K = 0 if the steel does not contain boron, K = 0.5 if the steel contains boron, in other words, If boron is added in an amount of 0.0005% or more, it is preferably higher than 3.2 and higher than 4.5 in order to obtain appropriate hardenability. In order to obtain a martensite-bainite structure without trace pearlite structures on parts that may be over 1000 mm thick and possibly as thick as 1500 mm, especially Tr must be higher than 4.5. Must;
- without compromising the machinability excessively, in order to obtain a suitable curing by the ^{carbides, Dr = 54xC 0.25 + 24.5x (} Mo * + 3xV *) 0.30 + 1.58xMn + 0.74xNi + 1.8xSi + 12.5x ( The value of Cr) ^0.20 must be between 85 and 95;
The value of U = 1600xC + 100x (0.25xCr + Mo * + 4.5xV *), which is an index of machinability (the lower U, the better the machinability) should be less than 10.0, preferably less than 9.0 ;
The value of R = 3.8 × C + 10 × Si + 3.3 × Mn + 2.4 × Ni + 1.4 × (Cr + Mo *), which depends on the thermal conductivity resistance , in other words the reciprocal of the thermal conductivity , should preferably be less than 2.7 × Tr. More preferably, the ratio R / (2.7 × Tr) should be 0.90 or less, even more preferably 0.80 or less. However, in view of all the requirements of the properties desired for steel, this value may not normally drop below 11 and therefore, as far as possible, the present invention is more specific. Relates to steels with R>11;
-The sum of Mo * + 3xV *, in view of all stresses, must exceed 0.4%, so the composition of the steel has a favorable analytical result, i.e.
0.230% ≦ C ≦ 0.350%
Si ≦ 0.30%
0.1% ≦ Mn ≦ 1.8%
Ni ≦ 25%
0.2% ≦ Cr ≦ 3%
Mo + W / 2 ≦ 2.5%
V + Nb / 2 + Ta / 4 ≦ 0.3%
The Mo * + 3 × V * must exceed 0.8%, and if this steel has a more favorable analytical result, ie
0.240% ≦ C ≦ 0.320%
Si ≦ 0.15%
0.1% ≦ Mn ≦ 1.6%
Ni ≦ 2%
0.2% ≦ Cr ≦ 2.5%
0.3% ≦ Mo + W / 2 ≦ 2.5%
V + Nb / 2 + Ta / 4 ≦ 0.3%
The Mo * + 3xV * must exceed 1.2%.

  In order to produce a mold with this steel, the steel is produced, cast, hot-rolled or hot-forged in a known manner, cut and cut to a thickness of more than 20 mm, or 100 mm. Get blocks that may reach over 400mm, possibly 600mm, and even 1500mm. It should be noted that at the thinnest thickness, the block may be a sheet or a large plate, and at the thickest thickness it is usually a forged block.

The block in particular depends on the thickness and hardenability of the steel so that the steel contains boron, and the block also obtains a martensite structure, or a martensite-bainite structure throughout the mass. When quenched in air, oil or water, it is austenitized at a temperature above AC ₃ , preferably below 950 ° C., optionally with forging or rolling heat. Finally, the blocks are tempered at a temperature above 500 ° C., preferably at least 550 ° C. but below AC ₁ . In this way, a hardness of between about 430 HB and 530 HB is obtained.

  In such a block, mold parts with polished and possibly granulated impressions are machined in a known manner. In some cases, these parts are surface hardened, for example, by gas nitriding. After gas nitriding, apart from the extremely nitrided surfaces of the parts, the hardness of the steel is between about 430HB and 530HB.

  By way of example and comparison, the analysis results summarized in Table 1 are considered, but some characteristics of the analysis results are summarized in Table 2.

  Examples 1-6, 9-12, and 14-16 correspond to the present invention, while Examples 17, 18, 20, and 21 are shown as comparisons. These steels do not contain selenium, tellurium, lead, bismuth or calcium additions. However, these steels contain a small amount of sulfur between 0.010% and 0.020%.

  For all these steels, the hardness HB is not only the hardness HVHAZ of the heat affected zone near the weld point compared to the hardness HV basicity of the basic metal not affected by heat, but in other words in the tempered and quenched state, in other words Measured for martensite structure or martensite-bainite structure tempered at 550 ° C. These results are also summarized in Table 1.

  These two tables show similar hardness (HB) and similar hardness coefficient Dr, and the steel according to the present invention has better machinability (lower U / Dr ratio) than the steel shown as a comparison. It shows that. In addition, these steels are more suitable for repair by welding, and have a low HAZ hardness, especially a low ratio of HVHAZ to basic HV, so they are shown as a comparison, especially for polishing after repair. It reacts more uniformly than steel. In the steel according to the invention, the HVHAZ / HV basic ratio does not actually exceed 1.20 when the carbon is below 0.35%.

これらの鋼は、プラスチック材料の射出成形用金型の部品を製造するのに適している。しかし、それらの鋼は、金属加工工具の部品を製造するのにも適している。

These steels are suitable for producing injection mold parts of plastic materials. However, these steels are also suitable for producing metalworking tool parts.

Claims (11)

It has a thickness of more than 20 mm, its structure is completely martensite or martensite-bainite, its hardness is in all respects between 430 HB and 530 HB, the chemical composition of the steel is weight% so,
0.180% ≦ C ≦ 0.350%
Si ≦ 0.15%
Mn ≦ 2.5%
Ni ≦ 3%
Cr ≦ 3.5%
Mo + W / 2 ≦ 2.8%
V + Nb / 2 + Ta / 4 ≦ 0.5%
Al ≦ 0.4%
Ti + Zr / 2 ≦ 0.1%
Boron with a content between 0.0005% and 0.015%,
Including
The balance is iron and inevitable impurities, copper is an impurity, the chemical composition also satisfies the following formula:
3.2 ≦ Tr ≦ 9
85 ≦ Dr ≦ 95
U / Dr ≦ 10.0
R / (2.7 × Tr) ≦ 0.80
Mo * + 3xV * ≧ 0.4%
In the formula, for the content represented by%,
Tr = 1.8xC + 1.1xMn + 0.7xNi + 0.6xCr + 1.6xMo * + K
Where K = 0.5,
Dr = 54xC ^0.25 + 24.5x (Mo * + 3xV *) ^0.30 + 1.58xMn + 0.74xNi + 1.8xSi + 12.5x (Cr) ^0.20
U = 1600 × C + 100 × (0.25 × Cr + Mo * + 4.5 × V *),
R = 3.8xC + 10xSi + 3.3xMn + 2.4xNi + 1.4x (Cr + Mo *),
Mo * = Mo + W / 2,
V * = V + Nb / 2 + Ta / 4,
The content of boron, aluminum, titanium, zirconium, and nitrogen, expressed as 1/1000 of the weight percent,

Where K1 = Min (I *; J *),
I * = Max (0; I), and J * = Max (0; J),
I = Min (N; N−0.29 (Ti + Zr / 2−5)),

Steel blocks for the production of molds for the injection molding of plastic materials or for the molding of metals or for the manufacture of metalworking parts. It has a thickness of more than 20 mm, its structure is completely martensite or martensite-bainite, its hardness is in all respects between 430 HB and 530 HB, the chemical composition of the steel is weight% so,
0.180% ≦ C ≦ 0.350%
Si ≦ 0.15%
Mn ≦ 2.5%
Ni ≦ 3%
Cr ≦ 3.5%
Mo + W / 2 ≦ 2.8%
V + Nb / 2 + Ta / 4 ≦ 0.5%
Al ≦ 0.4%
Ti + Zr / 2 ≦ 0.1%
Boron with a content between 0.0005% and 0.015%,
One or more elements from sulfur, selenium, and tellurium, the total content of these elements being 0.2% or less,
Including
The balance is iron and inevitable impurities, copper is an impurity, the chemical composition also satisfies the following formula:
3.2 ≦ Tr ≦ 9
85 ≦ Dr ≦ 95
U / Dr ≦ 10.0
R / (2.7 × Tr) ≦ 0.80
Mo * + 3xV * ≧ 0.4%
In the formula, for the content represented by%,
Tr = 1.8xC + 1.1xMn + 0.7xNi + 0.6xCr + 1.6xMo * + K
Where K = 0.5,
Dr = 54xC ^0.25 + 24.5x (Mo * + 3xV *) ^0.30 + 1.58xMn + 0.74xNi + 1.8xSi + 12.5x (Cr) ^0.20
U = 1600 × C + 100 × (0.25 × Cr + Mo * + 4.5 × V *),
R = 3.8xC + 10xSi + 3.3xMn + 2.4xNi + 1.4x (Cr + Mo *),
Mo * = Mo + W / 2,
V * = V + Nb / 2 + Ta / 4,
The content of boron, aluminum, titanium, zirconium, and nitrogen, expressed as 1/1000 of the weight percent,

Where K1 = Min (I *; J *),
I * = Max (0; I), and J * = Max (0; J),
I = Min (N; N−0.29 (Ti + Zr / 2−5)),

Steel blocks for the production of molds for the injection molding of plastic materials or for the molding of metals or for the manufacture of metalworking parts. It has a thickness of more than 20 mm, its structure is completely martensite or martensite-bainite, its hardness is in all respects between 430 HB and 530 HB, the chemical composition of the steel is weight% so,
0.180% ≦ C ≦ 0.350%
Si ≦ 0.15%
Mn ≦ 2.5%
Ni ≦ 3%
Cr ≦ 3.5%
Mo + W / 2 ≦ 2.8%
V + Nb / 2 + Ta / 4 ≦ 0.5%
Al ≦ 0.4%
Ti + Zr / 2 ≦ 0.1%
Boron with a content between 0.0005% and 0.015%,
One or more elements from lead and bismuth, the total content of these elements being 0.2% or less,
Including
The balance is iron and inevitable impurities, copper is an impurity, the chemical composition also satisfies the following formula:
3.2 ≦ Tr ≦ 9
85 ≦ Dr ≦ 95
U / Dr ≦ 10.0
R / (2.7 × Tr) ≦ 0.80
Mo * + 3xV * ≧ 0.4%
In the formula, for the content represented by%,
Tr = 1.8xC + 1.1xMn + 0.7xNi + 0.6xCr + 1.6xMo * + K
Where K = 0.5,
Dr = 54xC ^0.25 + 24.5x (Mo * + 3xV *) ^0.30 + 1.58xMn + 0.74xNi + 1.8xSi + 12.5x (Cr) ^0.20
U = 1600 × C + 100 × (0.25 × Cr + Mo * + 4.5 × V *),
R = 3.8xC + 10xSi + 3.3xMn + 2.4xNi + 1.4x (Cr + Mo *),
Mo * = Mo + W / 2,
V * = V + Nb / 2 + Ta / 4,
The content of boron, aluminum, titanium, zirconium, and nitrogen, expressed as 1/1000 of the weight percent,

Where K1 = Min (I *; J *),
I * = Max (0; I), and J * = Max (0; J),
I = Min (N; N−0.29 (Ti + Zr / 2−5)),

Steel blocks for the production of molds for the injection molding of plastic materials or for the molding of metals or for the manufacture of metalworking parts. It has a thickness of more than 20 mm, its structure is completely martensite or martensite-bainite, its hardness is in all respects between 430 HB and 530 HB, the chemical composition of the steel is weight% so,
0.180% ≦ C ≦ 0.350%
Si ≦ 0.15%
Mn ≦ 2.5%
Ni ≦ 3%
Cr ≦ 3.5%
Mo + W / 2 ≦ 2.8%
V + Nb / 2 + Ta / 4 ≦ 0.5%
Al ≦ 0.4%
Ti + Zr / 2 ≦ 0.1%
Boron with a content between 0.0005% and 0.015%,
Containing calcium with a content of 0.1% or less,
The balance is iron and inevitable impurities, copper is an impurity, the chemical composition also satisfies the following formula:
3.2 ≦ Tr ≦ 9
85 ≦ Dr ≦ 95
U / Dr ≦ 10.0
R / (2.7 × Tr) ≦ 0.80
Mo * + 3xV * ≧ 0.4%
In the formula, for the content represented by%,
Tr = 1.8xC + 1.1xMn + 0.7xNi + 0.6xCr + 1.6xMo * + K
Where K = 0.5,
Dr = 54xC ^0.25 + 24.5x (Mo * + 3xV *) ^0.30 + 1.58xMn + 0.74xNi + 1.8xSi + 12.5x (Cr) ^0.20
U = 1600 × C + 100 × (0.25 × Cr + Mo * + 4.5 × V *),
R = 3.8xC + 10xSi + 3.3xMn + 2.4xNi + 1.4x (Cr + Mo *),
Mo * = Mo + W / 2,
V * = V + Nb / 2 + Ta / 4,
The content of boron, aluminum, titanium, zirconium, and nitrogen, expressed as 1/1000 of the weight percent,

Where K1 = Min (I *; J *),
I * = Max (0; I), and J * = Max (0; J),
I = Min (N; N−0.29 (Ti + Zr / 2−5)),

Steel blocks for the production of molds for the injection molding of plastic materials or for the molding of metals or for the manufacture of metalworking parts.   5. The steel block according to claim 1, wherein the chemical composition is R> 11. 6. The steel block according to claim 1, wherein the silicon content is less than 0.15 % by weight and the carbon content is not more than 0.35% by weight.   The steel block according to claim 1, wherein U / Dr <9.0. Its composition is 0.230% ≦ C ≦ 0.350%
Si ≦ 0.15%
0.1% ≦ Mn ≦ 1.8%
Ni ≦ 2%
0.2% ≦ Cr ≦ 3%
Mo + W / 2 ≦ 2.5%
V + Nb / 2 + Ta / 4 ≦ 0.3%
Mo * + 3xV * ≧ 0.8%
The steel block according to claim 7, wherein Its composition is 0.240% ≦ C ≦ 0.320%
Si ≦ 0.15%
0.1% ≦ Mn ≦ 1.6%
Ni ≦ 2%
0.2% ≦ Cr ≦ 2.5%
0.3% ≦ Mo + W / 2 ≦ 2.5%
V + Nb / 2 + Ta / 4 ≦ 0.3%
Mo * + 3xV * ≧ 1.2%
The steel block according to claim 8, wherein:   The steel block according to claim 8, wherein Tr> 4.5.   11. A steel mold part machined into a block according to any one of claims 1 to 10, wherein at least a part of the surface is hardened by nitriding and its hardness is between 430HB and 530HB in all respects.